Color photography



Patented June 4, 1946 COLOR PHOTOGRAPHY Paul WrVittum and Lot S. Wilder, Rochester, N. Y., assignors to Eastman Kodak Company. Rochester, N. Y., acorporation of New Jersey Serial No. 528,456

No Drawing. Application March 28, 1944,

3 Claims. 1

as phenolic hydroxyl compounds or compounds,

with reactive methylene groups, which are capable of reacting with the development product of aromatic amino photographic developers to produce dyes, The color formers may be added directly'to the emulsion layers as described by Fischer or they may be incorporated in a separate medium which is insoluble in the carrier'for the sensitive silver halide as described in Mannes and Godowsky U. S. Patent 2,304,940 granted December 15, 1942, and Jelley and Vittum U. S. Patent 2,322,027, granted June 15, 1943.

A difficulty frequently encountered in these processes is the formation of color fog or stain. With materials in which color forming compounds are incorporated in the sensitive layer, dye fog is formed along with the customary silver fog met in black-and-white photography but in addition fog is also formed from any oxidized developer formed by the action of air, oxidizing silver removal baths, etc. It is well known that in these processes the dye is formed when the silver halide is reduced to metallic silver, thereby oxidizing the developing agent to a form which couples with the color former. Once the developing agent is oxidized, it couples immediately with the color former whether a. photographic image is present or not. Aerial oxidation of the developer or oxidation by means other than the photographic image, therefore, converts the developer to a form which will immediately react with the color former to produce a color fog or stain. Fog or stain arising from these causes is not readily controlled by the same procedures used to reduce or control silver ice.

It is, therefore, an object of the present invention to provide a means for stabilizing color forming developers toward aerial oxidation. A further object is to provide a means for reducing or eliminating the formation oi. color fog in photographic emulsions, particularly incorporated-coupler ing in a silver halide emulsion or in a color-forming developer solution, ascorbic acid in any of its tautomeric forms. 1 The ascorbicacid may be incorporated in a developing solution containing a coupler or in a color developing solution containing no coupler and intended to be used for the development of incorporated-coupler materials, these sensitive materials containing the coupler in the emulsion layer. .By color developer we mean a developing solution containing as the developing agent a primary aromatic amino developing agent such asdiethyl-paraphenylene-diamine.

We have found that color fog or stain in incorporated-coupler materials may be appreciably reduced by adding to the emulsion layers before coating or after coating and before processing an ascorbic acid, which has reducing properties and thereby tends to prevent the formation of color fog. It is believed that the ascorbic acid exerts an anti-oxidant action either by preventing the formation of extraneous oxidized developer or by reducing any extraneous oxidized developer before it has an opportunity to react with the color former. Whatever the mechanism of the reaction, .wehave found it possible in many cases to reduce markedly the fog or strain density without seriously affectingthe densities of the developed dye images. i

Compounds which we have found suitable for use according to our invention include 1-ascorbic acid and d-isoascorbic acid. These compounds have the following formula:

CH- H-CHzOH HOO/ When used in the emulsion layers, the ascorbic acid may be incorporated in a single layer coating or in one or more layers of a multi-layer coating. It may be desirable, for example, to have the ascorbic acid present in only one or two layers of a multi-layer coating. When the ascorbic acid is used with emulsions containing a coupler dissolved in agents insoluble in gelatin as in the processes described in Mannes and Godowsky U. S. Patent 2,304,940 and Jelley and Vittum U. S. Patent 2,322,027, it may be added either to the emulsion itself or to the coupler-carrier along with the coupler.

In general, the ascorbic acids may be used in the emulsion in quantities ranging from 0.1 gram to 1 gram per liter of gelatino-silver halide emulsion. When used in the developing solution or other bath, the quantities used may vary from 0.05 gram to 0.5 gram per liter of solution. These values are illustrative only.

The following examples illustrate color-forming developers containing ascorbic acid:

1. Diethyl p-phenylene dianiine grams 4.0 Potassium bromide ..do 1.0 Sodium sulfite "do--." 0.5 d-Iso-ascorbic acid -do 0.2

Sodium carbonate do 80.0 Water to liters 1.0

2. Diethyl p-phenylene diamine- "grams" 6.0 Potassium bromide do 2.0 d-Iso-ascorbic acid do 0.3 Sodium carbonate -do 80.0 Sodium hydroxide do- 4.0 Water to liters 1.0

3. Sodium hexametaphosphate ....grarns 1.0

.Soclium sulfite-. do 4.0

2-amino-5-diethylaminotoluene HCl l l grams 3.0 Sodium carbonate (anhydrous) do 10.0 Sodium metaborate do 40.0 Potassium bromide do 0.8 5-methyl benzotriazoleni; d0 0.03 d-Iso-ascorbic acid do 0.2

Water to H--. ....liters-'.. 1.0

4. Water -1. cc 800.0 Sodium'sulfite (anhydrous) grams 25.0 2-amino-5-diethylaminotoluene HCl grams" 1.2

Sodium carbonate do 20.0

Potassium bromide do 1.5

Sodium thiocyanate do 4.0

, Sodium hydroxide ..do 4.0

S-nitro-benzimidazole nitrate -do 0.30 2,6-dibromo 1,5 dihydroxy naphthalene grams.. 1.5

d-Iso-ascorbic acid -do.... 0.2

Water to liters 1.0

The reducing agent may be added to one of the film processing baths such as a prebath or the first developer bath. In the case oi negative development as disclosed. for example, in Jelley and Vittum U. S. Patent 2,322,027, the first deyeloper is a color-forming developer. The reducing agent may, therefore, be used in a color-forming developer such as a diethyl-p-phenylenediamine developer.

Our method is intended for use principally with emulsions which produce a negative image upon direct development, that is, emulsions in which a negative image would be formed upon development after exposure under a positive image or in which positive images would be formed on direct development after exposure under a negative image. It may also be used for reversal color development.

Our process is particularly useful with paper materials, where it is especially important to reduce the minimum (fog) densities. This applies ,both to negative-developed paper and to reversal paper and transparency materials.

It will be understood that the examplesand modifications disclosed herein are by way of example only and that our invention is to be taken as limited only by the scope of the appended claims.

We claim:

i 1. The method of preventing the formation of color fog in a photographic silver halide emulsion which contains a non-difiusing coupler therein, comprising developing said emulsion after exposure with a primary aromatic amino developing agent in the presence of an ascorbic acid. 2. The method of preventing the formation of color fog in a photographic silver halide emulsion which produces a negative image on development andwhich contains anon-diffusing coupler there in, comprising developing said emulsion after exposure with a primary aromatic amino developing agent in the presence of ascorbic acid.

3. The method of preventing the formation of color fog in a photographic silver halide emulsion which produces a negative image on development and which contains a non-diffusing coupler therein, comprising exposing said emulsion and developing it in a solution containing a primary aromatic amino developing agent and ascorbic acid.

PAUL W. VITTUM. LOTS. WILDER. 

